Precise biasing of analog-to-digital converters by means of auto-zero feedback

Auto-zero biasing refers to a technique whereby the DC bias in an analog-to-digital converter is controlled using negative feedback. A portion of the converter's digital output, typically the sign bit, is decoded locally, and the resulting analog signal is then averaged and subtracted from the input signal. This feedback controls the converter's bias with a precision that scales with the amplitude of the input. For small signals it is therefore possible to achieve almost arbitrarily precise biasing without precision circuit components. The properties of auto-zero control circuits are described, and the design of such circuits is illustrated by means of a /spl mu/-law PCM codec example.